1. Field of the Invention
The present invention relates to a focus condition sensing device which is provided with a CCD (charge coupled device).
2. Description of the Related Art
Conventionally, there is known a focus condition sensing device which can perform a multi-point distance measurement, in which distances from the camera to a plurality of points on an object to be photographed are detected. The focus condition sensing device is constructed in such a manner that plural photo-diodes linearly aligned on a CCD chip, are divided into three light receiving lines, for example. Each of the light receiving lines is used for measuring a distance from the camera to a center, right or left portion of the object, for example, and in the view-finder, marks indicating the three distance measurement points corresponding to the center, right and left portions are provided.
The distance measurement points in the view-finder are determined in accordance with a structure of the photo-diodes provided in the CCD. Thus, if the number of the distance measurement points are to be increased, for example, the CCD chip and the optical system should be newly designed, resulting in an undesirable design time and increased cost.
Therefore, an object of the present invention is to provide a focus sensing device including a plurality of imaging devices, which are generally used for a camera, and which can be freely designed to change a number of distance measurement points. In other words, in the present invention, the imaging devices need not be redesigned in order to accommodate the number of distance measurement points.
According to the present invention, there is provided a focus condition sensing device comprising first and second imaging device units, an accumulating operation control processor and an output control processor.
The first and second imaging device units output an electric charge, which is accumulated in accordance with an amount of light incident on the first and second imaging device units, as video signals. The accumulating operation control processor that controls an accumulating operation of the electric charge in the first and second imaging device units. The output control processor controls an output operation of the video signals by the first and second imaging device units. The output control processor starts the output operation on the first imaging device unit during the accumulating operation in the second imaging device unit.
Optionally, the accumulating operation control processor simultaneously starts the accumulating operations in the first and second imaging device units.
Preferably, the output control processor may sense first completion of the accumulating operation in the first imaging device unit, by changing a level of a control permission signal, by which a control of each of the first and second imaging device units is activated, during the accumulating operations in the first and second imaging device units.
Further optionally, the accumulating operation of the second imaging device unit may continue until the accumulating operation is completed, even if the output control processor senses that the accumulating operation in the first imaging device unit has been completed first. In this case, the second imaging device unit may keep electric charges therein until the output operation of the first imaging device unit is completed, even if the accumulating operation of the second imaging device unit is completed.
Still further, the output control processor may prohibit the output of the video signal from the second imaging device unit until the output of the video signal from the first imaging device unit is completed, even if the accumulating operation of the second imaging device unit is completed while the video signal is output from the first imaging device.